Up to now, as an external storage device for host equipment, such as portable information terminals, desktop computers, notebook computers, portable telephone sets, audio appliances or household electrical appliances, a card type small-sized removable IC memory, detachably mounted to these equipment and having enclosed therein a semiconductor memory, has been used.
This sort of the memory device has a nonvolatile semiconductor memory (IC memory), such as a flash memory, enclosed therein. In this semiconductor memory, various digital data, such as still image data, moving picture data, speech data or music data, are stored. The flash memory is a rewritable memory for repeatedly writing or erasing data. Thus, for the memory device, having enclosed therein the flash memory, a file management system of a routine hierarchical directory structure, exemplified by MS-DOS (trademark) format, premised on the use of the rewritable disc medium, may be used.
Meanwhile, the flash memory is a relatively costly device. Thus, by using a write-once type non-volatile semiconductor memory, such as PROM (programmable read-only memory), which is less costly than the flash memory, as a data storage device, a memory device can be fabricated at a lower cost.
If the write-once type non-volatile semiconductor memory is used in this manner as the data storage device for the memory device, it is more desirable for convenience to the user to supervise the files by the hierarchical directory structure, such as the MS-DOS (trademark) format, as in the case of the rewritable memory device employing the flash memory.
With the memory device, employing the write-once type semiconductor memory, as data storage device, it is not possible to erase the recorded entity data. For convenience to the user, the files etc. preferably can be pseudo-erased on the file management system.
Even in the memory device employing the write-once type semiconductor memory, as the data storage device, the readout processing itself is the same as that in the memory device employing the rewritable semiconductor memory. Thus, for convenience to the user, the physical structure and the file management system compatible with a conventional IC memory device, having the rewritable semiconductor memory, is desirable, insofar as data readout is concerned.